Method for recovering pigments from algal cultures

ABSTRACT

A method and apparatus ( 101 ) for the recovery of fat soluble compounds, such as beta carotene, is described. In one embodiment of the invention a solution ( 102 ) containing a fat soluble compound is passed through a fluidised bed ( 104 ) of crystalline metallic ore particles, such as magnetite, allowing the fat soluble compound to bind to the particles to form a complex ( 109 ). The fat soluble compound is released from the complex ( 109 ) by passing a wash solution ( 107 ) through the fluidised bed and subsequently collected in solution ( 108 ). The crystalline metallic ore particles may be reused.

FIELD

This invention relates to a method of recovering fat soluble compounds,including but not restricted to pigments such as beta-carotene, fromsolutions, including but not restricted to those solutions containingmicroalgal cells.

BACKGROUND

Intensive cultivation of microalgal cells is widely used as the sourceof a range of biological materials produced by algae including lipids,pigments and protein. A major limitation to the commercial feasibilityof manufacturing such materials using algal biotechnology is the factthat microalgal cells exist at relatively low concentrations in water,are of very small size and can be mechanically and osmotically fragile.The harvesting of algal cells and their products at a commercial scalerequires processes which concentrate the small algal cells and theirconstituent chemical products in an efficient manner which is simple,reliable and requires minimal energy inputs.

To date, methods which have been developed involve using either energyrequiring processes such as centrifugation and drying, or use low energyprocesses such as flocculation, settling or algal behavioural responseswhich are unreliable and inefficient. Other methods require thedisintegration of the algal cells which can render any cellularcomponents useless; for example, degradation of valuable components,such as the carotenoids, via oxidation can occur.

One example of a method which may be used to obtain certain cellularcomponents of algal cells, without any adverse degradation of thosecellular components, is described in the patent specification relatingto PCT/AU82/00165 entitled “Method for Harvesting Algae”. Thisspecification concentrates on methods for harvesting and concentratingalgae, including Dunaliella, from suspensions of a certain salinity,whereby the whole algal cells are adsorbed onto an appropriate adsorbentmedia The principle finding relating to this invention is that algalcell membranes become hydrophobic at salt concentrations above 3Menabling them to adsorb onto substances having a hydrophobic surface. Anumber of suitable hydrophobic adsorbents are described in thisspecification. In addition, a process of rendering certain adsorbentshydrophobic, or more hydrophobic, by treatment with silanes for exampleis described.

In PCT/AU82/00165 the whole-cell-adsorbent-media complex is thenprocessed using organic solvents which damage the cell membrane andpotentially which allow cellular components, such as beta-carotene, tobe released while the cellular debris and insoluble cell componentsremain adsorbed to the adsorbent media The beta-carotene released intothe organic solvent in this invention may contains contaminants such astriterpenoids and other lipids and thus further processing is requiredto isolate only the beta-carotene.

OBJECT

It is an object of the present invention to provide an improved methodof extracting fat-soluble compounds or at least to provide the publicwith a useful choice.

STATEMENT OF INVENTION

In one aspect of the present invention there is provided a method ofextracting fat-soluble compounds from aqueous solutions including thesteps:

providing an aqueous solution in which a fat-soluble compound ispresent;

providing a bed of crystalline metallic ore particles held in anappropriate vessel;

applying the aqueous solution to the bed of crystalline metallic oreparticles substantially near the bottom of the bed at a rate sufficientto form and maintain a fluidised bed of crystalline metallic oreparticles;

allowing the fat-soluble compound to attach to the crystalline metallicore particles to form a crystalline-metallic-ore-fat-soluble-compoundcomplex;

providing a wash solution;

contacting the wash solution with thecrystalline-metailic-ore-fat-soluble-compound complex to desorb thefat-soluble compound from the complex;

collecting the wash solution containing the fat-soluble compound; and

isolating the fat-soluble compound from the wash solution.

Preferably the crystalline metallic ore particles are magnetiteparticles.

Preferably the wash solution is contacted with thecrystalline-metallic-ore-fat-soluble-compound complex by applying thewash solution to the fluidised bed of crystalline metallic ore particlessubstantially near the bottom of the fluidised bed and at a ratesufficient to maintain the bed in a fluidised state and the resultantwash solution containing the fat-soluble compound is collected from nearthe top of, or above, the fluidised bed of crystalline metallic oreparticles.

Preferably the method further includes the step of collecting thecrystalline-metallic-ore-fat-soluble-compound complex prior to providinga wash solution and contacting the wash solution with thecrystalline-metallic-ore-fat-soluble-compound complex.

Preferably the crystalline-metallic-ore-fat-soluble-compound complex iscollected from a region substantially near the top of the fluidised bedof crystalline metallic ore particles by means of continuousdecantation.

Preferably the crystalline-metallic-ore-fat-soluble-compound complex isdried and stored for a period prior to being contacted with the washsolution.

Preferably the fat-soluble compound is present in the aqueous solutionwithin a number of cells and the aqueous solution is a culture media.

Preferably the cells are those of Dunaliella salina.

Preferably the fat-soluble compound is a natural pigment.

Preferably the pigment is a carotenoid.

Preferably the carotenoid is beta-carotene.

Preferably the wash solution is an organic solvent.

Preferably the fat-soluble compound is isolated from the wash solutionby evaporation or drying.

In another aspect of the present invention there is provided asubstantially pure fat-soluble compound obtained using the method of anyone of claims 1 to 13.

In yet another aspect of the present invention there is provided acrystalline-metallic-ore-fat-soluble-compound complex obtained using amethod as herein described.

FIGURES

These and other aspects of the present invention, which should beconsidered in all its novel aspects, will become apparent from thefollowing description of the preferred embodiment of the invention,which are given by way of example only, with reference to theaccompanying figure in which:

FIG. 1 illustrates a preferred extraction apparatus and method accordingto the present invention; and

FIG. 2 illustrates a preferred extraction apparatus and alternativemethod according to the present invention.

PREFERRED EMBODIMENT

The preferred embodiment of the invention is described below in terms ofthe recovery of beta-carotene from water containing the microalgalspecies Dunaliella salina (D.salina). It will be appreciated by those ofgeneral skill in the art that the invention would be applicable to therecovery of the other carotenoids and to other fat-soluble pigments fromD.salina, and to the recovery of carotenoids or other fat-solublecompounds or pigments from other suitable organisms. The process of thepresent invention may also be applicable to the extraction from anaqueous solution of fat-soluble compounds suspended therein.

Throughout the following description the words adsorption andabsorption, or derivatives thereof, such as adsorb or absorb, are used.The word adsorb is used to describe how a substance can be held on thesurface of another and the word absorb to refer to the inclusion orincorporation of one substance into another. These words have been usedinterchangeably in the following text as the interactions between thesubstances (beta-carotene and magnetite) may be referred to in eitherway. In addition, the word attach is used to cover both adsorption andabsorption. Those of general skill in the art will appreciate thisfactor.

General Principles of the Preferred Embodiment of the Invention

Beta-carotene, is one of a group of compounds called carotenoids; thisgroup also includes alpha carotene, lutene, lutene monoepoxide,astaxanthin, zeaxanthin, canthaxanthin, and lycopene. These compoundsare well characterised and those skilled in the art will recognise themas being coloured fat-soluble compounds which finction as part of thelight-capturing apparatus in photosynthetic pathways. Beta-carotene, inparticular, is a precursor to vitamin A, a vitamin obtained from dietarysources, rather than de novo, in animals. In addition, the carotenoidfamily have been associated with antioxidant activities. As a result,carotenoids and in particular, beta-carotene, are sought after for usein many food and health products.

The microalgae Dunaliella are typically cultivated in water which has ahigh concentration of dissolved salts, particularly concentrates ofseawater such as those used for the production of salt by solarevaporation. Such waters are very corrosive of metal which they comeinto contact with. Under conditions of optimal nutrient concentrations,moderate temperatures and intense solar radiation, Dunaliella can growto concentrations of one million algal cells per ml. The individualcells can contain up to 10% of their weight as beta-carotene, and thusbeta-carotene can accumulate to the extent of 15 mg per litre of brine.The rest of Dunaliella cell biomass is composed of protein,carbohydrates and other lipids.

The process of the present invention uses an absortion medium,magnetite, which absorbs betacarotene with very high affinity, but doesnot absorb significant anounts of the other components of the cell mass.However, beta-carotene is a lipid which is contained within the cellmembrane, as opposed to being secreted from the cell and thus free insolution, therefore Dunaliella cell membranes must be disrupted beforethe beta-carotene is available for absorption.

Magnetite is a crystalline iron ore which has a surface of sharp edgeswith numerous cracks, crags and irregularities. It has been identifiedthat in the present invention magnetite can be used for the dual purposeof disrupting cell membranes and absorbing beta-carotene. WhenDunaliella cells are brought into contact with magnetite particles thecell membrane is punctured by the numerous sharp edges and the cellcontents are disgorged into the bulk growth/culture medium.

Another hitherto undescribed property of magnetite is that, because ofits unique structure, it selectively absorbs beta-carotene. This occursas beta-carotene, being a lipid, is insoluble in water and the surfaceof magnetite crystals are somewhat hydrophobic in nature. Whenbetacarotene is present in an environment of brine and magnetite, itpartitions towards the more hydrophobic solid phase than the hydrophilicliquid phase. When the surface of crags within the magnetite particlebecome coated in beta carotene, a more hydrophobic microenvironment iscreated in which further beta carotene is absorbed. The total loading ofbeta-carotene into magnetite is thus very high; for example 2% to 4% ofthe mass of the magnetite. At this concentration, the void spaces withinthe magnetite structures are filled with beta-carotene. It will beunderstood by those of general skill in the art that it will not alwaysbe appropriate to load the magnetite completely as it may impact on thedownstream recovery of beta-carotene.

Yet another useful property of magnetite disclosed herein is that whenbeta-carotene is adsorbed onto, then absorbed into magnetite, theoxidation processes which ordinarily cause the rapid decay ofbeta-carotene, particularly when it is exposed to oxygen, are inhibitedsuch that the magnetite/beta-carotene complex is very stable and doesnot degrade when exposed to heat or when it is dried.

Because of the above identified properties of magnetite which are notobvious, magnetite. provides an ideal material upon which to collect andconcentrate beta-carotene. However, it will be appreciated by those ofgeneral skill in the art that alternative absorption media, such asanother crystalline metallic ore which has properties equivalent tothose of magnetite, for example hematite, may be used in the process ofthe present invention.

As indicated above when beta carotene has been absorbed on magnetiteuntil the magnetite is saturated, the material is, for example, around2% by weight beta-carotene. As the brine containing D. salina typicallyhas a maximum betasarotene concentration of 20 parts per million,absorption by the magnetite, in this example, thus concentrates thebeta-carotene by a factor of one thousand fold. Magnetite typically hasa bulk density of 4 Kg per litre whereas the brine used for growingbeta-carotene-containing D.salina has a bulk density typically of 1.2 Kgper litre. Therefore by passing 1,000 litres of brine containing D.salina through one kilogram of magnetite, all the beta-carotene can beremoved and contained in a volume of 250 ml, a concentration of almost4,000 fold.

The beta-carotene can be easily desorbed from the magnetite by simplywashing the magnetite with a suitable wash solution such as an organicsolvent. Both polar and non-polar solvents are suitable for thispurpose. Ordinarily non-polar solvents would not easily mix with amaterial such as magnetite when it is wetted with water or brine due tohydrophobicity. However, another useful feature of the microcrystallinestructure of magnetite is that interfacial tension is broken by thesharp surface, thus a non-polar solvent is easily able to penetrate, andthen dewater the magnetite.

The organic solvent used to desorb beta-carotene will containessentially pure beta carotene, as other microalgal products are notabsorbed onto the magnetite. Because the solvent contains purebeta-carotene it is particularly easy to remove the beta carotene andrecover the solvent for re-use, for example by using reduced pressuredevices such as crystallisers.

Solvents which are suitable for desorbing beta-carotene from magnetiteinclude, but are not restricted to acetone, ethanol, hexane, petroleumether, or any mixtures of these solvent. Further, due to consumer demandfor natural products it is preferable that natural solvents be used. Inthis regard we have found terpene alcohols to be efficient solvents foruse in this invention; for example, cineol (eucalyptus oil), d-limonene(lemon oil), citral (citrus oil) and terpen-4-ol (tee tree oil).

Basic Apparatus and Extraction Example of the Preferred Embodiment ofthe Invention

An example of an apparatus in which the process of the preferred form ofthe invention may be conducted is shown in Diagram/FIG. 1 and FIG. 2. InFIG. 1 the magnetite is contained within a conical vessel (101). Themagnetite sits on a distribution plate, or plenum, (110) which separatesthe inlet pipe (103) from the vessel interior. This plenum (110) allowsa solid phase of magnetite to settle onto the bottom of the vessel whenthe apparatus is not in use. Brine containing D. Salina (102) isintroduced at the bottom of the conical vessel via inlet pipe (103) atsuch a flow rate as to maintain the magnetite as a fluidised bed (104).Being a fluidised bed contactor, there is no prospect for the adsorptionmedia, magnetite, to become clogged. The brine (containing cellulardebris) (105) leaves the vessel at outlet pipe (106). It can either besent into another similar vessel to (101) if it still containsunabsorbed Beta-carotene, or it can be returned to the algal growthpond.

One can see from FIG. 1 that the fluidised bed separates into twodifferent layers or phases. The bottom phase contains primarilymagnetite particles and the top phase magnetite-betacarotene complexes(109); which move upwards because of a change in their density due toforming the complex with beta-carotene. It will be appreciated by thoseof general skill in the art that the layers may not be distinct from oneanother as illustrated in FIGS. 1 and 2 and that while two layers doform they do so across a gradient as a result of the degree of loadingof magnetite with beta-carotene. Further, it will be appreciated thatthe size of the magnetite particle and the velocity of fluid flowinginto the vessel will have an effect on the position of that particlewithin the vessel. The Figures have been simplified to illustrate thatmagnetite loaded with beta-carotene will decrease in density during theprocess.

It should be noted that magnetite of various particle sizes may be usedin the present invention. The size of such particles is not important inrelation to the absorption of beta-arotene but it will have an effect onthe behaviour of the fluidised bed (104). Thus, as a result of theparticle size of the magnetite used the flow rate of solutions into thevessel (101) may be required to be altered to maintain the bed (104) ina fluidised state.

The beta-carotene can be desorbed from the magnetite in the top phase bychanging the flow into the inlet at (103) from brine to the desorptionsolvent (107) of choice. A different flow rate is required to keep themagnetised bed fluidised due to the density differences between brineand the solvent. The solvent effluent (108) from (106) containsessentially pure beta-carotene which can be recovered by evaporating thesolvent During this stage magnetite present in the top phase may fall tothe bottom phase as the beta-carotene is released and its densityincreases.

It can be clearly seen that by using a number of vessels such as (101),connected in series such that the outlet (106) of one is connected tothe inlet (103) of the next vessel in the series, any number of vesselscan be connected to each other. If both the inlet and the outlet areconnected via a manifold which can feed either brine or desorptionsolvent into the vessel, then a continuous process cycle ofadsorption/desorption/adsorption is possible.

Such a system operates at low pressure, has only valves as moving parts,can be constructed of cheap plastic material and has a very low energyrequirement. As such, this system provides a very simple, efficient andreliable means of harvesting beta-carotene from brine.

FIG. 2 uses the same apparatus as FIG. 1 but illustrates an alternativeembodiment in which when the magnetite has become progressively loadedwith beta-carotene the magnetite-betacarotene complex (109) is collectedfrom the vessel (101) at outlet (106). At this stage the complex can bewashed immediately with an appropriate solvent or stored at roomtemperature for prolonged periods without any significant deteriorationof the contained beta-carotene and washed at a later date.

These basic examples will become farther apparent from the specificexamples 1 to 3 which follow.

SPECIFIC EXAMPLES RELATING TO THE PREFERRED EMBODIMENT OF THE INVENTIONExample 1

A culture of Dunaliella salina was grown in outdoor ponds containingsodium chloride at a concentration of 60 g per litre (approximately 1M). When the culture had attained a beta-carotene concentration of 9 mgper litre, the culture was pumped into the bottom of a vertical perspexcylinder of 100 mm diameter at a rate of 1.5 litre per minute. When thecylinder became filled with liquid, 800 g of magnetite (120 mesh) wasintroduced into the top of the cylinder. The magnetic moved towards thebottom of the cylinder but became suspended within the cylinder as afluidised bed which maintained a height of 400 mm. When the fluidisedbed became stable, the culture which passed through the bed to the topof the cylinder was sampled and the beta carotene concentration wasmeasured and found to be 3.9 mg per litre.

While the culture medium was still being pumped through the bottom ofthe cylinder, a further 400 g of magnetite was then introduced into thetop of the cylinder. The fluidised bed then expanded to a height of 580mm. The culture emerging from the top of the cylinder was again sampledand this time found to have a beta carotene concentration of 1.9 mg perlitre. A further 400 g of magnetite was then added to the cylinder whichcaused the fluidised bed height to increase to 750 mm. At this bedheight the culture emerging from the top of the bed appeared clear. Thebeta carotene concentration was measured and found to be 0.04 mg perlitre.

After approximately 1 hour of operation with a total added volume ofmagnetite of 1,600 g, and a constant upward culture medium flow rate of1.5 litres per minute, the fluidised bed volume had expanded to 780 mm,and had separated into two distinct zones. The upper zone had a slightlyred colour and was 65 mm high. The lower zone was the same black colouras the originally formed fluidised bed and was 715 mm high. There was adistinct boundary between the two layers.

Magnetite material from the upper layer was collected using a pipette,then washed with fresh water-and examined under a microscope. There wasno sign of any algal cells adhering to this magnetite. The magnetite wasthen dried in a flow of warm air, weighed accurately and the washed withacetone. The acetone was collected and the beta carotene concentrationin the acetone was determined by measuring the optical density at 450 nmwavelength. It was determined in this way that the magnetite contained3.9% by weight beta carotene.

Example 2

A culture of Dunaliella salina was grown in outdoor ponds containingsodium chloride at a concentration of 60 g per litre (approximately 1 M)and magnesium chloride at 60 g per litre (approximately 0.6 M). When theculture had attained a beta carotene concentration of 11 mg per litre,the culture was pumped into the bottom of a vertical perspex cylinder of100 mm diameter at a rate of 1.4 litre per minute. When the cylinderbecame filled with liquid, 1,600 g of magnetite (120 mesh) wasintroduced into the top of the cylinder. The magnetite moved towards thebottom of the cylinder but became suspended within the cylinder as thefluidised bed which maintained a height of 800 mm. When the fluidisedbed became stable, the culture which passed through the bed to the topof the cylinder was sampled and the beta carotene concentration wasmeasured and found to be 0.07 mg per litre. The culture medium emergingfrom the top of the column was examined under a microscope. There wereno intact algal cells observed, however cellular debris, comprisingmostly broken cell membranes, and halobacteria were observed.

After approximately 2 hour of operation at a constant upward culturemedium flow rate of 1.4 litres per minute, the fluidised bed volume hadexpanded to 845 mm, and had separated into two distinct zones. The upperzone had a slightly red colour and was 165 mm high. At this height themagnetic fluidised bed had reached the top of the perspex cylinder. Asthe bed expanded further, the top layer spilled over and was collectedand was examined under a microscope. There was no sign of any algalcells adhering to this magnetite. The magnetite was then dried in a flowof warm air, weighed accurately and then washed with acetone. Theacetone was collected and the beta carotene concentration in the acetonewas determined by measuring the optical density at 450 nm wavelength. Inthis way it was determined that the magnetite contained 3.8% by weightbeta carotene.

Example 3

A culture of Dunaliella salina was grown in outdoor ponds containingsodium chloride at a concentration of 90 g per litre (approximately 1.5M) and magnesium chloride at 90 g per litre (approximately 1.0 M). Whenthe culture had attained a beta carotene concentration of 14 mg perlitre, the culture was pumped into the bottom of a vertical perspexcylinder of 100 mm diameter at a rate of 1.65 litre per minute. When thecylinder became filled with liquid, 1,600 g of magnetite (120 mesh) wasintroduced into the top of the cylinder. The magnetite moved towards thebottom of the cylinder but became suspended within the cylinder as afluidised bed which maintained a height of 800 mm. When the fluidisedbed became stable, the culture which passed through the bed to the topof the cylinder was sampled and the beta carotene concentration wasmeasured and found to be 0.06 mg per litre.

In this example the cylinder was modified by creating a spillway 950 mmup the length of the cylinder. After 95 minutes of operation, the upper(red) zone of the fluidised magnetite bed had reached the spillway, andmagnetite began trickling from the spillway. This spilled magnetite wasseparated from the culture medium by decantation. The rate of flow ofmagnetite trickling from the cylinder was estimated by collecting thematerial for one minute, removing the culture medium by decantation andweighing the magnetite. It was found that approximately 600 mg ofmagnetite was spilling from the cylinder each minute. By washing themagnetite with acetone and measuring the optical density of the washingacetone at 450 nm, the spilled magnetite was found to contain 3.65% byweight beta carotene.

For the next 4 hours a 6 g sample of fresh magnetite was added to thetop of the cylinder every 10 minutes. The fresh magnetite could be seento travel through the upper red zone into the lower black zone of thefluidised bed. For the 4 hours during which the trial was undertaken,the fluidised bed maintained a more-or-less constant height and a quiteconstant rate of red magnetite spillage from the spillway. At thecompletion of the trial, 400 litres of culture medium had been passedthrough the cylinder and substantially all the beta-carotene had beenremoved.

The fluid flow into the cylinder was then switched from culture mediumat 1.65 litres per minute to cineole at a flow rate of 2.25 litres perminute. Again a fluidised bed was formed, this time with a bed height of820 mm. The cineole emerging from the top of the cylinder was a deep redcolour. Spectrophotometric measurement of the cineole at 450 nm showedit contained beta carotene at a concentration of 1.35% w/v. After aboutfour minutes of flow, the cineole emerging from the top of the cylinderbecame a paler red, and after 6 minutes it was clear. All the elutedcineole was collected, and evaporated using a rotary evaporator. As thecineol evaporated, dark crystals of beta carotene were formed. When thecineole had completely evaporated, the remaining crystalline materialwas collected and weighed. The material weighed 5.44 g.

It can be concluded that the 400 litres of culture originally applied tothe magnetite fluidised bed contained 5.6 g of beta carotene. Of this,5.44 g was recovered in crystalline form from the cineole eluent. Thisrepresents a recovery of over 97% of the original beta carotene presentin the culture.

Industrial Application and Advantages

Carotenoids and other fat-soluble pigments are sought after additivesfor food and health products. The process of the present invention isvery simple, requires little more energy than that needed to reticulatewater containing microalgae to the apparatus and thus provides anefficient means of extracting these compounds from their source and thusmay prove of commercial and economic advantage.

The process has the further advantage of stabilising the product andenabling the convenient storage of the product as a concentrate.

What is claimed is:
 1. A method of extracting fat-soluble compounds fromaqueous solutions comprising the steps of: providing an aqueous solutionin which a fat-soluble compound is present; providing a bed ofcrystalline metallic ore particles held in a vessel; applying theaqueous solution to the bed of crystalline metallic ore particlessubstantially near the bottom of the bed at a rate sufficient to formand maintain a fluidized bed of crystalline metallic ore particles,wherein the fat-soluble compound is absorbed or adsorbed by thecrystalline metallic ore particles to formcrystalline-metallic-ore-fat-soluble-compound complex particles, whereinthe bulk density of the particulatecrystalline-metallic-ore-fat-soluble-compound complex is less than thatof the particulate metallic ore, and wherein the fluidized bed forms anupper and a lower zone, the lower zone substantially comprisingcrystalline metallic ore particles and the upper zone substantiallycomprising crystalline-metallic-ore-fat-soluble-compound complexparticles; collecting the crystalline-metallic-ore-fat-soluble-compoundcomplex particles from the upper zone of the fluidized bed; providing awash solution; contacting the wash solution with thecrystalline-metallic-ore-fat-soluble-compound complex particles todesorb the fat-soluble compound; collecting the wash solution containingthe fat-soluble compound; and isolating the fat-soluble compound fromthe wash solution.
 2. The method as claimed in claim 1, wherein thecrystalline metallic ore particles are magnetite particles.
 3. Themethod as claimed in claim 1, wherein thecrystalline-metallic-ore-fat-soluble-compound complex is collected bymeans of continuous decantation.
 4. The method as claimed in claim 1,wherein the crystalline-metallic-ore-fat-soluble-compound complexparticles are dried and stored for a period prior to being contactedwith the wash solution.
 5. A method as claimed in claim 1, wherein thefat-soluble compound is present in the aqueous solution with a number ofcells and the aqueous solution is a culture media.
 6. A method asclaimed in claim 5, wherein the cells are those of Dunaliella salina (D.salina).
 7. A method as claimed in claim 5, wherein the culture media isbrine.
 8. A method as claimed in claim 1, wherein the fat-solublecompound is a natural pigment.
 9. A method as claimed in claim 8,wherein the pigment is a carotenoid.
 10. A method as claimed in claim 9,wherein the carotenoid is beta-carotene.
 11. A method of extractingfat-soluble compounds selected from the group consisting of betacarotene, alpha carotene, lutene, lutene monoepoxide, astaxanthin,zeaxanthin, canthaxanthin and lycopene from aqueous solutions containingD. salina cells comprising the steps of: providing an aqueous solutioncontaining D. salina cells in which said fat-soluble compound ispresent; providing a bed of crystalline metallic ore particles held in avessel; applying the aqueous solution containing the D. salina cells tothe bed of crystalline metallic ore particles substantially near thebottom of the bed at a rate sufficient to form and maintain a fluidizedbed of crystalline metallic ore particles so that the D. salina cellsare ruptured to release said fat-soluble compound, wherein saidfat-soluble compound is absorbed or adsorbed by the crystalline metallicore particles to form crystalline-metallic-ore-fat-soluble compoundcomplex particles, wherein the bulk density of the said complex is lessthan that of the particulate metallic ore, and wherein the fluidized bedforms an upper and a lower zone, the lower zone substantially comprisingcrystalline metallic ore particles and the upper zone substantiallycomprising said complex particles; collecting said complex particlesfrom the upper zone of the fluidized bed; providing a wash solution;contacting the wash solution with said complex particles to desorb thefat-soluble compound; collecting the wash solution containing thefat-soluble compound; and isolating the fat-soluble compound from thewash solution.
 12. The method as claimed in claim 11, wherein thecrystalline metallic ore particles are magnetite particles.
 13. Themethod as claimed in claim 11, wherein the complex is collected by meansof continuous decantation.
 14. The method as claimed in claim 11,wherein the complex particles are dried and stored for a period prior tobeing contacted with the wash solution.
 15. A method as claimed in claim11, wherein the aqueous solution is a culture media.
 16. A method asclaimed in claim 11, wherein the aqueous solution is brine.
 17. A methodas claimed in claim 11, wherein the fat-soluble compound is betacarotene.
 18. A method of extracting beta carotene from aqueoussolutions containing D. salina cells comprising the steps of: providingan aqueous solution containing D. salina cells in which the betacarotene is present; providing a bed of crystalline metallic oreparticles held in a vessel; applying the aqueous solution containing theD. salina cells to the bed of crystalline metallic ore particlessubstantially near the bottom of the bed at a rate sufficient to formand maintain a fluidized bed of crystalline metallic ore particles suchthat the D. salina cells are ruptured to release the beta carotene,wherein the beta carotene is absorbed or adsorbed by the crystallinemetallic ore particles to form crystalline-metallic-ore-beta carotenecomplex particles, wherein the bulk density of the particulatecrystalline-metallic-ore-beta carotene complex is less than that of theparticulate metallic ore, and wherein the fluidized bed forms an upperand a lower zone, the lower zone substantially comprising crystallinemetallic ore particles and the upper zone substantially comprisingcrystalline-metallic-ore-beta carotene complex particles; collecting thecrystalline-metallic-ore-beta carotene complex particles from the upperzone of the fluidized bed; providing a wash solution; contacting thewash solution with the crystalline-metallic-ore-beta carotene complexparticles to desorb the beta carotene; collecting the wash solutioncontaining the beta carotene; and isolating the beta carotene from thewash solution.
 19. The method as claimed in claim 18, wherein thecrystalline metallic ore particles are magnetite particles.
 20. Themethod as claimed in claim 18, wherein the complex is collected by meansof continuous decantation.
 21. The method as claimed in claim 18,wherein the complex particles are dried and stored for a period prior tobeing contacted with the wash solution.
 22. A method as claimed in claim18, wherein the aqueous solution is a culture media.
 23. A method asclaimed in claim 18, wherein the aqueous solution is brine.